Pneumatic tire and method for producing same

ABSTRACT

A pneumatic tire and a method for producing the pneumatic tire, wherein the pneumatic tire includes a generally string-shaped adhesive sealant, the sealant is continuously and spirally attached at least to the inner periphery of the tire that corresponds to a tread portion, the sealant has a wider portion on at least one of the longitudinal ends thereof, and the wider portion has a width larger than that of the longitudinally adjoining portion.

TECHNICAL FIELD

The present invention relates to a pneumatic tire and a method forproducing the pneumatic tire.

BACKGROUND ART

Self-sealing tires with sealants applied to the inner peripheriesthereof have been known as puncture resistant pneumatic tires(hereinafter, pneumatic tires are also referred to simply as tires).Sealants automatically seal puncture holes formed in such self-sealingtires.

Self-sealing tires may be produced by spraying an adhesive sealant ontothe inner periphery of a tire or by circumferentially spirally attachinga generally string-shaped adhesive sealant to the inner periphery of atire. Among these, the latter method is considered to be advantageousfor preventing the deterioration of tire uniformity and providing betterweight balance.

However, since the generally string-shaped sealant has a certain degreeof viscosity to avoid flowing, it may show insufficient adhesion.Unfortunately, such a sealant may be difficult to attach to the innerperiphery of a tire, and particularly the attachment start portion ofthe sealant can easily peel off.

SUMMARY OF INVENTION Technical Problem

The present invention aims to solve the above problems and provide apneumatic tire (self-sealing tire) in which the attachment start portionof the sealant does not easily peel off, and a method for producing theself-sealing tire.

Solution to Problem

The present invention relates to a pneumatic tire (self-sealing tire),including a generally string-shaped adhesive sealant, the sealant beingcontinuously and spirally attached at least to an inner periphery of thetire that corresponds to a tread portion, the sealant having a widerportion at at least one of longitudinal ends thereof, the wider portionhaving a width larger than that of a longitudinally adjoining portion.

The width of the wider portion is preferably 103% to 180% of a width ofthe sealant other than the wider portion.

The sealant other than the wider portion preferably has a width of 1.3to 13 mm.

The sealant other than the wider portion preferably has a substantiallyconstant width.

The wider portion of the sealant preferably has a length shorter than500 mm.

An area where the sealant is attached preferably has a width that is 80%to 120% of a tread contact width.

The sealant preferably has a thickness of 1 to 10 mm.

The present invention also relates to a method for producing a pneumatictire (self-sealing tire), the method including discharging a generallystring-shaped adhesive sealant from a nozzle to continuously andspirally attach the sealant at least to an inner periphery of a tirethat corresponds to a tread portion, the sealant being attached underconditions where a distance between the inner periphery of the tire anda tip of the nozzle is adjusted to a distance d₁ and then to a distanced₂ larger than the distance d₁ so that at least one of longitudinal endsof the sealant forms a wider portion having a width larger than that ofa longitudinally adjoining portion.

The sealant is preferably extruded from a twin screw kneading extruderand fed to the nozzle.

ADVANTAGEOUS EFFECTS OF INVENTION

In the pneumatic tire (self-sealing tire) of the present invention, aportion of the sealant that corresponds to starting of attachment iswider to prevent peeling of this portion of the sealant. In the methodfor producing a self-sealing tire of the present invention, the distancebetween the inner periphery of a tire and the tip of the nozzle isshortened at the beginning of the attachment to allow the self-sealingtire to be easily produced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory view schematically showing an example of anapplicator used in a method for producing a self-sealing tire.

FIG. 2 is an enlarged view showing the vicinity of the tip of the nozzleincluded in the applicator shown in FIG. 1.

FIG. 3 is an explanatory view schematically showing the positionalrelationship of the nozzle to the tire.

FIG. 4 is an explanatory view schematically showing an example of agenerally string-shaped sealant continuously and spirally attached tothe inner periphery of the tire.

FIGS. 5A and 5B are enlarged views showing the vicinity of the tip ofthe nozzle included in the applicator shown in FIG. 1.

FIG. 6 is an explanatory view schematically showing an example of asealant attached to a self-sealing tire.

FIG. 7 is an explanatory view schematically showing an example of aproduction facility used in a method for producing a self-sealing tire.

FIG. 8 is an explanatory view schematically showing an example of across section of the sealant shown in FIG. 4 when the sealant is cutalong the straight line A-A orthogonal to the direction along which thesealant is applied (the longitudinal direction).

FIG. 9 is an explanatory view schematically showing an example of across section of a pneumatic tire.

DESCRIPTION OF EMBODIMENTS

The pneumatic tire (self-sealing tire) of the present invention ischaracterized by including a generally string-shaped adhesive sealant,wherein the sealant is continuously and spirally attached at least tothe inner periphery of the tire that corresponds to a tread portion, thesealant has a wider portion at at least one of the longitudinal endsthereof, and the wider portion has a width larger than that of thelongitudinally adjoining portion.

In the self-sealing tire of the present invention, a portion of thesealant that corresponds to starting of attachment has a larger width toimprove adhesion of this portion so that peeling of this portion of thesealant can be prevented.

The method for producing a self-sealing tire of the present invention isintended to produce the above self-sealing tire and is characterized byattaching a sealant under conditions where the distance between theinner periphery of a tire and the tip of the nozzle is adjusted to adistance d₁ and then to a distance d₂ larger than the distance d₁.

In the method for producing a self-sealing tire of the presentinvention, the distance between the inner periphery of a tire and thetip of the nozzle is shortened at the beginning of the attachment, sothat the width of the sealant corresponding to the attachment startportion can be increased to allow the self-sealing tire to be easilyproduced.

First, suitable examples of the method for producing a self-sealing tireof the present invention (see particularly the second embodiment) willbe described.

The following describes suitable examples of the method for producing aself-sealing tire of the present invention.

A self-sealing tire can be produced, for example, by preparing a sealantby mixing the components of the sealant, and then attaching the sealantto the inner periphery of a tire by application or other means to form asealant layer. The self-sealing tire includes the sealant layer locatedradially inside an innerliner.

The hardness (viscosity) of the sealant needs to be adjusted to anappropriate viscosity according to the service temperature bycontrolling the rubber component and the degree of crosslinking. Therubber component is controlled by varying the type and amount of liquidrubber, plasticizers, or carbon black, while the degree of crosslinkingis controlled by varying the type and amount of crosslinking agents orcrosslinking activators.

Any sealant that shows adhesion may be used, and rubber compositionsconventionally used to seal punctures of tires can be used. The rubbercomponent constituting a main ingredient of such a rubber compositionmay include a butyl-based rubber. Examples of the butyl-based rubberinclude butyl rubber (IIR) and halogenated butyl rubbers (X-IIR) such asbrominated butyl rubber (Br-IIR) and chlorinated butyl rubber (Cl-IIR).In particular, in view of fluidity and other properties, either or bothof butyl rubber and halogenated butyl rubbers can be suitably used. Thebutyl-based rubber to be used is preferably in the form of pellets. Sucha pelletized butyl-based rubber can be precisely and suitably suppliedto a continuous kneader so that the sealant can be produced with highproductivity.

In order to reduce the deterioration of the fluidity of the sealant, thebutyl-based rubber to be used is preferably a butyl-based rubber Ahaving a Mooney viscosity ML₁₊₈ at 125° C. of at least 20 but less than40 and/or a butyl-based rubber B having a Mooney viscosity ML₁₊₈ at 125°C. of at least 40 but not more than 80. It is particularly suitable touse at least the butyl-based rubber A. When the butyl-based rubbers Aand B are used in combination, the blending ratio may be appropriatelychosen.

The Mooney viscosity ML₁₊₈ at 125° C. of the butyl-based rubber A ismore preferably 25 or more, still more preferably 28 or more, but morepreferably 38 or less, still more preferably 35 or less. If the Mooneyviscosity is less than 20, the fluidity may be reduced. If the Mooneyviscosity is 40 or more, the effect of the combined use may not beachieved.

The Mooney viscosity ML₁₊₈ at 125° C. of the butyl-based rubber B ismore preferably 45 or more, still more preferably 48 or more, but morepreferably 70 or less, still more preferably 60 or less. If the Mooneyviscosity is less than 40, the effect of the combined use may not beachieved. If the Mooney viscosity is more than 80, sealing performancemay be reduced.

The Mooney viscosity ML₁₊₈ at 125° C. is determined in conformity withJIS K-6300-1:2001 ata test temperature of 125° C. using an L type rotorwith a preheating time of one minute and a rotation time of eightminutes.

The rubber component may be a combination with other ingredients such asdiene rubbers, including natural rubber (NR), polyisoprene rubber (IR),polybutadiene rubber (BR), styrene-butadiene rubber (SBR),styrene-isoprene-butadiene rubber (SIBR), ethylene-propylene-dienerubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber(NBR), and butyl rubber (IIR). In view of fluidity and other properties,the amount of the butyl-based rubber based on 100% by mass of the rubbercomponent is preferably 90% by mass or more, more preferably 95% by massor more, particularly preferably 100% by mass.

Examples of the liquid polymer used in the sealant include liquidpolybutene, liquid polyisobutene, liquid polyisoprene, liquidpolybutadiene, liquid poly-α-olefin, liquid isobutylene, liquidethylene-α-olefin copolymers, liquid ethylene-propylene copolymers, andliquid ethylene-butylene copolymers. In order to provide adhesion andother properties, liquid polybutene is preferred among these. Examplesof the liquid polybutene include copolymers having a long-chainhydrocarbon molecular structure which is based on isobutene and furtherreacted with normal butene. Hydrogenated liquid polybutene may also beused.

In order to prevent the sealant from flowing during high-speed running,the liquid polymer (e.g. liquidpolybutene) to be used is preferably aliquid polymer A having a kinematic viscosity at 100° C. of 550 to 625mm²/s and/or a liquid polymer B having a kinematic viscosity at 100° C.of 3,540 to 4,010 mm²/s, more preferably a combination of the liquidpolymers A and B.

The kinematic viscosity at 100° C. of the liquid polymer A (e.g. liquidpolybutene) is preferably 550 mm²/s or higher, more preferably 570 mm²/sor higher. If the kinematic viscosity is lower than 550 mm²/s, flowingof the sealant may occur. The kinematic viscosity at 100° C. ispreferably 625 mm²/s or lower, more preferably 610 mm²/s or lower. Ifthe kinematic viscosity is higher than 625 mm²/s, the sealant may havehigher viscosity and deteriorated extrudability.

The kinematic viscosity at 100° C. of the liquid polymer B (e.g. liquidpolybutene) is preferably 3,600 mm²/s or higher, more preferably 3,650mm²/s or higher. If the kinematic viscosity is lower than 3,540 mm²/s,the sealant may have too low a viscosity and easily flow during serviceof the tire, resulting in deterioration of sealing performance oruniformity.

The kinematic viscosity at 100° C. is preferably 3,900 mm²/s or lower,more preferably 3,800 mm²/s or lower. If the kinematic viscosity ishigher than 4,010 mm²/s, sealing performance may deteriorate.

The kinematic viscosity at 40° C. of the liquid polymer A (e.g. liquidpolybutene) is preferably 20,000 mm²/s or higher, more preferably 23,000mm²/s or higher. If the kinematic viscosity is lower than 20,000 mm²/s,the sealant may be soft so that its flowing can occur. The kinematicviscosity at 40° C. is preferably 30,000 mm²/s or lower, more preferably28,000 mm²/s or lower. If the kinematic viscosity is higher than 30,000mm²/s, the sealant may have too high a viscosity and deterioratedsealing performance.

The kinematic viscosity at 40° C. of the liquid polymer B (e.g. liquidpolybutene) is preferably 120,000 mm²/s or higher, more preferably150,000 mm²/s or higher. If the kinematic viscosity is lower than120,000 mm²/s, the sealant may have too low a viscosity and easily flowduring service of the tire, resulting in deterioration of sealingperformance or uniformity. The kinematic viscosity at 40° C. ispreferably 200,000 mm²/s or lower, more preferably 170,000=²/s or lower.If the kinematic viscosity is higher than 200,000 mm²/s, the sealant mayhave too high a viscosity and deteriorated sealing performance.

The kinematic viscosity is determined in conformity with JIS K 2283-2000at 100° C. or 40° C.

The amount of the liquid polymer (the combined amount of the liquidpolymers A and B and other liquid polymers) relative to 100 parts bymass of the rubber component is preferably 50 parts by mass or more,more preferably 100 parts by mass or more, still more preferably 150parts by mass or more. If the amount is less than 50 parts by mass,adhesion may be reduced. The amount is preferably 400 parts by mass orless, more preferably 300 parts by mass or less, still more preferably250 parts by mass or less. If the amount is more than 400 parts by mass,flowing of the sealant may occur.

In the case where the liquid polymers A and B are used in combination,the blending ratio of these polymers [(amount of liquid polymerA)/(amount of liquid polymer B)] is preferably 10/90 to 90/10, morepreferably 30/70 to 70/30, still more preferably 40/60 to 60/40. Whenthe blending ratio is within the range indicated above, the sealant isprovided with good adhesion.

The organic peroxide (crosslinking agent) is not particularly limited,and conventionally known compounds can be used. The use of a butyl-basedrubber and a liquid polymer in an organic peroxide crosslinking systemimproves adhesion, sealing performance, fluidity, and processability.

Examples of the organic peroxide include acyl peroxides such as benzoylperoxide, dibenzoyl peroxide, and p-chlorobenzoyl peroxide; peroxyesterssuch as 1-butyl peroxyacetate, t-butyl peroxybenzoate, and t-butylperoxyphthalate; ketone peroxides such as methyl ethyl ketone peroxide;alkyl peroxides such as di-t-butyl peroxybenzoate and 1,3-bis(1-butylperoxyisopropyl)benzene; hydroperoxides such as t-butylhydroperoxide; and dicumyl peroxide and t-butylcumyl peroxide. In viewof adhesion and fluidity, acyl peroxides are preferred among these, withdibenzoyl peroxide being particularly preferred. Moreover, the organicperoxide (crosslinking agent) to be used is preferably in the form ofpowder. Such a powdered organic peroxide (crosslinking agent) can beprecisely and suitably supplied to a continuous kneader so that thesealant can be produced with high productivity.

The amount of the organic peroxide (crosslinking agent) relative to 100parts by mass of the rubber component is preferably 0.5 parts by mass ormore, more preferably 1 part by mass or more, still more preferably 5parts by mass or more. If the amount is less than 0.5 parts by mass,crosslink density may decrease so that flowing of the sealant can occur.The amount is preferably 40 parts by mass or less, more preferably 20parts by mass or less, still more preferably 15 parts by mass or less.If the amount is more than 40 parts by mass, crosslink density mayincrease so that the sealant can be hardened and show reduced sealingperformance.

The crosslinking activator (vulcanization accelerator) to be used may beat least one selected from the group consisting of sulfenamidecrosslinking activators, thiazole crosslinking activators, thiuramcrosslinking activators, thiourea crosslinking activators, guanidinecrosslinking activators, dithiocarbamate crosslinking activators,aldehyde-amine crosslinking activators, aldehyde-ammonia crosslinkingactivators, imidazoline crosslinking activators, xanthate crosslinkingactivators, and quinone dioxime compounds (quinoid compounds). Forexample, quinone dioxime compounds (quinoid compounds) can be suitablyused. The use of a butyl-based rubber and a liquid polymer in acrosslinking system including a crosslinking activator added to anorganic peroxide improves adhesion, sealing performance, fluidity, andprocessability.

Examples of the quinone dioxime compound include p-benzoquinone dioxime,p-quinone dioxime, p-quinone dioxime diacetate, p-quinone dioximedicaproate, p-quinone dioxime dilaurate, p-quinone dioxime distearate,p-quinone dioxime dicrotonate, p-quinone dioxime dinaphthenate,p-quinone dioxime succinate, p-quinone dioxime adipate, p-quinonedioxime difuroate, p-quinone dioxime dibenzoate, p-quinone dioximedi(o-chlorobenzoate), p-quinone dioxime di(p-chlorobenzoate), p-quinonedioxime di(p-nitrobenzoate), p-quinone dioxime di(m-nitrobenzoate),p-quinone dioxime di(3,5-dinitrobenzoate), p-quinone dioximedi(p-methoxybenzoate), p-quinone dioxime di(n-amyloxybenzoate), andp-quinone dioxime di(m-bromobenzoate). In view of adhesion, sealingperformance, and fluidity, p-benzoquinone dioxime is preferred amongthese. Moreover, the crosslinking activator (vulcanization accelerator)to be used is preferably in the form of powder. Such a powderedcrosslinking activator (vulcanization accelerator) can be precisely andsuitably supplied to a continuous kneader so that the sealant can beproduced with high productivity.

The amount of the crosslinking activator (e.g. quinone dioximecompounds) relative to 100 parts by mass of the rubber component ispreferably 0.5 parts by mass or more, more preferably 1 part by mass ormore, still more preferably 3 parts by mass or more. If the amount isless than 0.5 parts by mass, flowing of the sealant may occur. Theamount is preferably 40 parts by mass or less, more preferably 20 partsby mass or less, still more preferably 15 parts by mass or less. If theamount is more than 40 parts by mass, sealing performance may bereduced.

The sealant may further contain an inorganic filler such as carbonblack, silica, calcium carbonate, calcium silicate, magnesium oxide,aluminum oxide, barium sulfate, talc, or mica; or a plasticizer such asaromatic process oils, naphthenic process oils, or paraffinic processoils.

The amount of the inorganic filler relative to 100 parts by mass of therubber component is preferably 1 part by mass or more, more preferably10 parts by mass or more. If the amount is less than 1 part by mass,sealing performance may be reduced due to degradation by ultravioletrays. The amount is preferably 50 parts by mass or less, more preferably40 parts by mass or less, still more preferably 30 parts by mass orless. If the amount is more than 50 parts by mass, the sealant may havetoo high a viscosity and deteriorated sealing performance.

In order to prevent degradation by ultraviolet rays, the inorganicfiller is preferably carbon black. In this case, the amount of thecarbon black relative to 100 parts by mass of the rubber component ispreferably 1 part by mass or more, more preferably 10 parts by mass ormore. If the amount is less than 1 part by mass, sealing performance maybe reduced due to degradation by ultraviolet rays. The amount ispreferably 50 parts by mass or less, more preferably 40 parts by mass orless, still more preferably 25 parts by mass or less. If the amount ismore than 50 parts by mass, the sealant may have too high a viscosityand deteriorated sealing performance.

The amount of the plasticizer relative to 100 parts by mass of therubber component is preferably 1 part by mass or more, more preferably 5parts by mass or more. If the amount is less than 1 part by mass, thesealant may show lower adhesion to tires, failing to have sufficientsealing performance. The amount is preferably 40 parts by mass or less,more preferably 20 parts by mass or less. If the amount is more than 40parts by mass, the sealant may slide in thekneader so that it cannot beeasily kneaded.

The sealant is preferably prepared by mixing a pelletized butyl-basedrubber, a powdered crosslinking agent, and a powdered crosslinkingactivator, and more preferably by mixing a pelletized butyl-basedrubber, a liquid polybutene, a plasticizer, carbon black powder, apowdered crosslinking agent, and a powdered crosslinking activator. Suchraw materials can be suitably supplied to a continuous kneader so thatthe sealant can be produced with high productivity.

The sealant is preferably obtained by incorporating a rubber componentincluding butyl rubber with predetermined amounts of a liquid polymer,an organic peroxide, and a crosslinking activator.

A sealant obtained by incorporating butyl rubber with a liquid polymersuch as liquid polybutene, especially wherein the butyl rubber and theliquid polymer are each a combination of two or more materials havingdifferent viscosities, can achieve a balanced improvement in adhesion,sealing performance, fluidity, and processability. This is because theintroduction of a liquid polymer component to an organic peroxidecrosslinking system using butyl rubber as the rubber component providesadhesion, and especially the use of liquid polymers or solid butylrubbers having different viscosities reduces flowing of the sealantduring high-speed running. Therefore, the sealant can achieve a balancedimprovement in adhesion, sealing performance, fluidity, andprocessability.

The viscosity at 40° C. of the sealant is not particularly limited. Inorder to allow the sealant to suitably maintain a generally string shapewhen it is applied to the inner periphery of a tire, and in view ofadhesion, fluidity, and other properties, the viscosity at 40° C. ispreferably 3,000 Pa·s or higher, more preferably 5,000 Pa·s or higher,but preferably 70,000 Pa·s or lower, more preferably 50,000 Pa·s orlower. If the viscosity is lower than 3,000 Pa·s, the applied sealantmay flow when the tire stops rotating, so that the sealant cannotmaintain the film thickness. Also, if the viscosity is higher than70,000 Pa·s, the sealant cannot be easily discharged from the nozzle.

The viscosity of the sealant is determined at 40° C. in conformity withJIS K 6833 using a rotational viscometer.

A self-sealing tire including a sealant layer located radially inside aninnerliner can be produced by preparing a sealant by mixing theaforementioned materials, and applying the sealant to the innerperiphery of a tire, and preferably to the radially inner face of aninnerliner. The materials of the sealant may be mixed using knowncontinuous kneaders, for example. In particular, they are preferablymixed using a co-rotating or counter-rotating multi-screw kneadingextruder, and especially a twin screw kneading extruder.

The continuous kneader (especially twin screw kneading extruder)preferably has a plurality of supply ports for supplying raw materials,more preferably at least three supply ports, still more preferably atleast three supply ports including upstream, midstream, and downstreamsupply ports. By sequentially supplying the raw materials to thecontinuous kneader (especially twin screw kneading extruder), the rawmaterials are mixed and sequentially and continuously prepared into asealant.

Preferably, the raw materials are sequentially supplied to thecontinuous kneader (especially twin screw kneading extruder), startingfrom the material having a higher viscosity. In this case, the materialscan be sufficiently mixed and prepared into a sealant of a consistentquality. Moreover, powder materials, which improve kneadability, shouldbe introduced as upstream as possible.

The organic peroxide is preferably supplied to the continuous kneader(especially twin screw kneading extruder) through its downstream supplyport. In this case, the time period from supplying the organic peroxideto applying the sealant to a tire can be shortened so that the sealantcan be applied to a tire before it is cured. This allows for more stableproduction of self-sealing tires.

Since kneading is unsuccessfully accomplished when a large amount of theliquid polymer is introduced at once into the continuous kneader(especially twin screw kneading extruder), the liquid polymer ispreferably supplied to the continuous kneader (especially twin screwkneading extruder) through a plurality of supply ports. In this case,the sealant can be more suitably kneaded.

When a continuous kneader (especially twin screw kneading extruder) isused, the sealant is preferably prepared using the continuous kneader(especially twin screw kneading extruder) having at least three supplyports by supplying a rubber component such as a butyl-based rubber, aninorganic filler, and a crosslinking activator each from an upstreamsupply port, a liquid polymer B from a midstream supply port, and aliquid polymer A, an organic peroxide, and a plasticizer each from adownstream supply port of the continuous kneader (especially twin screwkneading extruder), followed by kneading and extrusion. The materialssuch as liquid polymers may be entirely or partly supplied from therespective supply ports. Preferably, 95% by mass or more of the entireamount of each material is supplied from the supply port.

Preferably, all the raw materials to be introduced into the continuouskneader are introduced into the continuous kneader under the control ofa quantitative feeder. This allows for continuous and automatedpreparation of the sealant.

Any feeder that can provide quantitative feeding may be used, includingknown feeders such as screw feeders, plunger pumps, gear pumps, andmohno pumps.

Solid raw materials (especially pellets or powder) such as pelletizedbutyl-based rubbers, carbon black powder, powdered crosslinking agents,and powdered crosslinking activators are preferably quantitativelysupplied using a screw feeder. This allows the solid raw materials to besupplied precisely in fixed amounts, thereby leading to the productionof a higher quality sealant and therefore a higher quality self-sealingtire.

Moreover, the solid raw materials are preferably individually suppliedthrough separate respective feeders. In this case, the raw materialsneed not to be blended beforehand, which facilitates supply of thematerials in the mass production.

The plasticizer is preferably quantitatively supplied using a plungerpump. This allows the plasticizer to be supplied precisely in a fixedamount, thereby leading to the production of a higher quality sealantand therefore a higher quality self-sealing tire.

The liquid polymer is preferably quantitatively supplied using a gearpump. This allows the liquid polymer to be supplied precisely in a fixedamount, thereby leading to the production of a higher quality sealantand therefore a higher quality self-sealing tire.

The liquid polymer to be supplied is preferably kept under constanttemperature control. The constant temperature control allows the liquidpolymer to be supplied more precisely in a fixed amount. The liquidpolymer to be supplied preferably has a temperature of 20° C. to 90° C.,more preferably 40° C. to 70° C.

In view of easy mixing and extrudability, the mixing in the continuouskneader (especially twin screw kneading extruder) is preferably carriedout at a barrel temperature of 30° C. (preferably 50° C.) to 150° C.

In view of sufficient mixing, preferably, the materials suppliedupstream are mixed for 1 to 3 minutes, and the materials suppliedmidstream are mixed for 1 to 3 minutes, while the materials supplieddownstream are preferably mixed for 0.5 to 2 minutes in order to avoidcrosslinking. The times for mixing the materials each refer to theresidence time in the continuous kneader (especially twin screw kneadingextruder) from supply to discharge. For example, the time for mixing thematerials supplied downstream means the residence time from when theyare supplied through a downstream supply port until they are discharged.

By varying the screw rotational speed of the continuous kneader(especially twin screw kneading extruder) or the setting of atemperature controller, the temperature of the sealant discharged fromthe outlet can be controlled and therefore the rate of curingacceleration of the sealant can be controlled. As the screw rotationalspeed of the continuous kneader (especially twin screw kneadingextruder) increases, kneadability and material temperature increase. Thescrew rotational speed does not affect the discharge amount. In view ofsufficient mixing and control of the rate of curing acceleration, thescrew rotational speed is preferably 50 to 700 (preferably 550) rpm.

In view of sufficient mixing and control of the rate of curingacceleration, the temperature of the sealant discharged from the outletof the continuous kneader (especially twin screw kneading extruder) ispreferably 70° C. to 150° C., more preferably 90° C. to 130° C. When thetemperature of the sealant is within the range indicated above, thecrosslinking reaction begins upon the application of the sealant and thesealant adheres well to the inner periphery of a tire and, at the sametime, the crosslinking reaction more suitably proceeds, whereby aself-sealing tire having high sealing performance can be produced.Moreover, the crosslinking step described later is not required in thiscase.

The amount of the sealant discharged from the outlet of the continuouskneader (especially twin screw kneading extruder) is determinedaccording to the amounts of the raw materials supplied through thesupply ports. The amounts of the raw materials supplied through thesupply ports are not particularly limited, and a person skilled in theart can appropriately select the amounts. In order to suitably produce aself-sealing tire having much better uniformity and sealing performance,preferably a substantially constant amount (discharge amount) of thesealant is discharged from the outlet.

Herein, the substantially constant discharge amount means that thedischarge amount varies within a range of 93% to 107%, preferably 97% to103%, more preferably 98% to 102%, still more preferably 99% to 101%.

The outlet of the continuous kneader (especially twin screw kneadingextruder) is preferably connected to a nozzle. Since the continuouskneader (especially twin screw kneading extruder) can discharge thematerials at a high pressure, the prepared sealant can be attached in athin, generally string shape (bead shape) to a tire by means of a nozzle(preferably a small diameter nozzle creating high resistance) mounted onthe outlet. Specifically, by discharging the sealant from a nozzleconnected to the outlet of the continuous kneader (especially twin screwkneading extruder) and sequentially applying it to the inner peripheryof a tire, the applied sealant has a substantially constant thickness,thereby preventing deterioration of tire uniformity. This leads to theproduction of a self-sealing tire that is excellent in weight balance.The diameter of the discharge port of the nozzle (nozzle diameter) isnot particularly limited but is preferably 0.3 to 10.0 mm, morepreferably 0.5 to 8.0 mm, still more preferably 1.5 to 4.5 mm.

Next, for example, the mixed sealant is discharged from the nozzleconnected to the outlet of the extruder such as a continuous kneader(especially twin screw kneading extruder) to feed and apply the sealantdirectly to the inner periphery of a vulcanized tire, whereby aself-sealing tire can be produced. In this case, since the sealant whichhas been mixed in, for example, a twin screw kneading extruder and inwhich the crosslinking reaction in the extruder is suppressed isdirectly applied to the tire inner periphery, the crosslinking reactionof the sealant begins upon the application, and thus the sealant adhereswell to the tire inner periphery and, at the same time, the crosslinkingreaction suitably proceeds. For this reason, the sealant applied to thetire inner periphery suitably forms a sealant layer while maintaining agenerally string shape. Accordingly, the sealant can be applied andprocessed in a series of steps and therefore productivity is furtherimproved. Moreover, the application of the sealant to the innerperiphery of a vulcanized tire further enhances the productivity ofself-sealing tires. Furthermore, the sealant discharged from the nozzleconnected to the outlet of the continuous kneader (especially twin screwkneading extruder) is preferably sequentially applied directly to theinner periphery of a tire. In this case, since the sealant in which thecrosslinking reaction in the continuous kneader (especially twin screwkneading extruder) is suppressed is directly and continuously applied tothe tire inner periphery, the crosslinking reaction of the sealantbegins upon the application and the sealant adheres well to the tireinner periphery and, at the same time, the crosslinking reactionsuitably proceeds, whereby a self-sealing tire that is excellent inweight balance can be produced with higher productivity.

With regard to the application of the sealant to the inner periphery ofa tire, the sealant may be applied at least to the inner periphery of atire that corresponds to a tread portion, and more preferably at leastto the inner periphery of a tire that corresponds to a breaker. Omittingthe application of the sealant to areas where the sealant is unnecessaryfurther enhances the productivity of self-sealing tires.

The inner periphery of a tire that corresponds to a tread portion refersto a portion of the inner periphery of a tire that is located radiallyinside a tread portion which contacts the road surface. The innerperiphery of a tire that corresponds to a breaker refers to a portion ofthe inner periphery of a tire that is located radially inside a breaker.The breaker refers to a component placed inside a tread and radiallyoutside a carcass. Specifically, it is a component shown as a breaker 16in FIG. 9, for example.

Unvulcanized tires are usually vulcanized using bladders. During thevulcanization, such a bladder inflates and closely attaches to the innerperiphery (innerliner) of the tire. Hence, a mold release agent isusually applied to the inner periphery (innerliner) of the tire to avoidadhesion between the bladder and the inner periphery (innerliner) of thetire after completion of the vulcanization.

The mold release agent is usually a water-soluble paint or amold-releasing rubber. However, the presence of the mold release agenton the inner periphery of a tire may impair the adhesion between thesealant and the inner periphery of the tire. For this reason, it ispreferred to preliminarily remove the mold release agent from the innerperiphery of the tire. In particular, the mold release agent is morepreferably preliminarily removed at least from a portion of the tireinner periphery in which application of the sealant begins. Still morepreferably, the mold release agent is preliminarily removed from theentire area of the tire inner periphery where the sealant is to beapplied. In this case, the sealant adheres better to the tire innerperiphery and therefore a self-sealing tire having higher sealingperformance can be produced.

The mold release agent may be removed from the tire inner periphery byany method, including known methods such as buffing treatment, lasertreatment, high pressure water washing, or removal with detergents andpreferably with neutral detergents.

An example of a production facility used in the method for producing aself-sealing tire will be briefly described below referring to FIG. 7.

The production facility includes a twin screw kneading extruder 60, amaterial feeder 62 for supplying raw materials to the twin screwkneading extruder 60, and a rotary drive device 50 which fixes androtates a tire 10 while moving the tire in the width and radialdirections of the tire. The twin screw kneading extruder 60 has fivesupply ports 61, specifically, including three upstream supply ports 61a, one midstream supply port 61 b, and one downstream supply port 61 c.Further, the outlet of the twin screw kneading extruder 60 is connectedto a nozzle 30.

The raw materials are sequentially supplied from the material feeder 62to the twin screw kneading extruder 60 through the supply ports 61 ofthe twin screw kneading extruder 60 and then kneaded in the twin screwkneading extruder 60 to sequentially prepare a sealant. The preparedsealant is continuously discharged from the nozzle 30 connected to theoutlet of the twin screw kneading extruder 60. The tire is traversedand/or moved up and down (moved in the width direction and/or the radialdirection of the tire) while being rotated by the tire drive device, andthe sealant discharged from the nozzle 30 is sequentially applieddirectly to the inner periphery of the tire, whereby the sealant can becontinuously and spirally attached to the tire inner periphery. In otherwords, the sealant can be continuously and spirally attached to theinner periphery of a tire by sequentially applying the sealantcontinuously discharged from the continuous kneader (especially twinscrew kneading extruder) directly to the inner periphery of the tirewhile rotating and simultaneously moving the tire in the width directionand/or the radial direction of the tire.

Such a continuous and spiral attachment of the sealant to the tire innerperiphery can prevent deterioration of tire uniformity, thereby leadingto the production of a self-sealing tire that is excellent in weightbalance. Moreover, the continuous and spiral attachment of the sealantto the tire inner periphery allows for the formation of a sealant layerin which the sealant is uniformly provided in the circumferential andwidth directions of the tire, and especially in the circumferentialdirection of the tire. Thus, self-sealing tires having excellent sealingperformance can be stably produced with high productivity. The sealantis preferably attached without overlapping in the width direction, morepreferably without gaps. In this case, the deterioration of tireuniformity can be further prevented and a more uniform sealant layer canbe formed.

The raw materials are sequentially supplied to a continuous kneader(especially twin screw kneading extruder) which sequentially prepares asealant. The prepared sealant is continuously discharged from a nozzleconnected to the outlet of the continuous kneader (especially twin screwkneading extruder), and the discharged sealant is sequentially applieddirectly to the inner periphery of a tire. In this manner, self-sealingtires can be produced with high productivity.

The sealant layer is preferably formed by continuously and spirallyapplying a generally string-shaped sealant to the inner periphery of atire. In this case, a sealant layer formed of a generally string-shapedsealant provided continuously and spirally along the inner periphery ofa tire can be formed on the inner periphery of the tire. The sealantlayer may be formed of layers of the sealant, but preferably consists ofone layer of the sealant.

In the case of a generally string-shaped sealant, a sealant layerconsisting of one layer of the sealant can be formed by continuously andspirally applying the sealant to the inner periphery of a tire. In thecase of a generally string-shaped sealant, since the applied sealant hasa certain thickness, even a sealant layer consisting of one layer of thesealant can prevent the deterioration of tire uniformity and allow forthe production of a self-sealing tire having an excellent weight balanceand good sealing performance. Moreover, since it is sufficient to onlyapply one layer of the sealant without stacking layers of the sealant, aself-sealing tire can be produced with higher productivity.

The number of turns of the sealant around the inner periphery of thetire is preferably 20 to 70, more preferably 20 to 60, still morepreferably 35 to 50, because then the deterioration of tire uniformitycan be prevented and a self-sealing tire having an excellent weightbalance and good sealing performance can be produced with higherproductivity. Here, two turns means that the sealant is applied suchthat it makes two laps around the inner periphery of the tire. In FIG.4, the number of turns of the sealant is six.

The use of a continuous kneader (especially twin screw kneadingextruder) enables the preparation (kneading) of a sealant and thedischarge (application) of the sealant to be simultaneously andcontinuously performed. Thus, a highly viscous and adhesive sealantwhich is and difficult to handle can be directly applied to the innerperiphery of a tire without handling it, so that a self-sealing tire canbe produced with high productivity. When a sealant is prepared bykneading with a curing agent in a batch kneader, the time period frompreparing a sealant to attaching the sealant to a tire is not constant.In contrast, by sequentially preparing a sealant by mixing raw materialsincluding an organic peroxide using a continuous kneader (especiallytwin screw kneading extruder), and sequentially applying the sealant tothe inner periphery of a tire, the time period from preparing a sealantto attaching the sealant to a tire is held constant. Accordingly, whenthe sealant is applied through a nozzle, the amount of the sealantdischarged from the nozzle is stable; furthermore, the sealant showsconsistent adhesion while reducing the deterioration of adhesion to thetire, and even a highly viscous and adhesive sealant which is difficultto handle can be precisely applied to the tire inner periphery.Therefore, self-sealing tires of a consistent quality can be stablyproduced.

The following describes methods for applying the sealant to the innerperiphery of a tire.

First Embodiment

According to a first embodiment, a self-sealing tire can be produced,for example, by performing the Step (1), Step (2), and Step (3) below inthe process of applying an adhesive sealant through a nozzle to theinner periphery of a tire while rotating the tire and simultaneouslymoving at least one of the tire and nozzle in the width direction of thetire: Step (1) of measuring the distance between the inner periphery ofthe tire and the tip of the nozzle using a non-contact displacementsensor; Step (2) of moving at least one of the tire and nozzle in theradial direction of the tire according to the measurement to adjust thedistance between the inner periphery of the tire and the tip of thenozzle to a predetermined length; and Step (3) of applying the sealantto the inner periphery of the tire after the distance is adjusted.

The distance between the inner periphery of the tire and the tip of thenozzle can be maintained at a constant length by measuring the distancebetween the inner periphery of the tire and the tip of the nozzle usinga non-contact displacement sensor and feeding back the measurement.Moreover, since the sealant is applied to the tire inner periphery whilemaintaining the distance at a constant length, the applied sealant canhave a uniform thickness without being affected by variations in tireshape and irregularities at joint portions or the like. Furthermore,since it is not necessary to enter the coordinate data of each tirehaving a different size as in the conventional art, the sealant can beefficiently applied.

FIG. 1 is an explanatory view schematically showing an example of anapplicator used in a method for producing a self-sealing tire, and FIG.2 is an enlarged view showing the vicinity of the tip of the nozzleincluded in the applicator shown in FIG. 1.

FIG. 1 shows a cross section of a part of a tire 10 in the meridionaldirection (a cross section taken along a plane including the width andradial directions of the tire). FIG. 2 shows a cross section of a partof the tire 10 taken along a plane including the circumferential andradial directions of the tire. In FIGS. 1 and 2, the width direction(axis direction) of the tire is indicated by an arrow X, thecircumferential direction of the tire is indicated by an arrow Y, andthe radial direction of the tire is indicated by an arrow Z.

The tire 10 is mounted on a rotary drive device (not shown) which fixesand rotates a tire while moving the tire in the width and radialdirections of the tire. The rotary drive device allows for the followingindependent operations: rotation around the axis of the tire, movementin the width direction of the tire, and movement in the radial directionof the tire.

The rotary drive device includes a controller (not shown) capable ofcontrolling the amount of movement in the radial direction of the tire.The controller may be capable of controlling the amount of movement inthe width direction of the tire and/or the rotational speed of the tire.

A nozzle 30 is attached to the tip of an extruder (not shown) and can beinserted into the inside of the tire 10. Then an adhesive sealant 20extruded from the extruder is discharged from the tip 31 of the nozzle30.

A non-contact displacement sensor 40 is attached to the nozzle 30 tomeasure a distance d between the inner periphery 11 of the tire 10 andthe tip 31 of the nozzle 30.

Thus, the distance d to be measured by the non-contact displacementsensor is the distance in the radial direction of the tire between theinner periphery of the tire and the tip of the nozzle.

According to the method for producing a self-sealing tire of thisembodiment, the tire 10 formed through a vulcanization step is firstmounted on the rotary drive device, and the nozzle 30 is inserted intothe inside of the tire 10. Then, as shown in FIG. 1 and FIG. 2, the tire10 is rotated and simultaneously moved in the width direction while thesealant 20 is discharged from the nozzle 30, whereby the sealant iscontinuously applied to the inner periphery 11 of the tire 10. The tire10 is moved in the width direction according to the pre-entered profileof the inner periphery 11 of the tire 10.

The sealant 20 preferably has a generally string shape as describedlater. More specifically, the sealant preferably maintains a generallystring shape when the sealant is applied to the inner periphery of thetire. In this case, the generally string-shaped sealant 20 iscontinuously and spirally attached to the inner periphery 11 of the tire10.

The generally string shape as used herein refers to a shape having acertain width, a certain thickness, and a length longer than the width.FIG. 4 schematically shows an example of a generally string-shapedsealant continuously and spirally attached to the inner periphery of thetire, and FIG. 8 schematically shows an example of a cross section ofthe sealant shown in FIG. 4 when the sealant is cut along the straightline A-A orthogonal to the direction along which the sealant is applied(longitudinal direction). Thus, the generally string-shaped sealant hasa certain width (length indicated by W in FIG. 8) and a certainthickness (length indicated by D in FIG. 8). The width of the sealantmeans the width of the applied sealant. The thickness of the sealantmeans the thickness of the applied sealant, more specifically thethickness of the sealant layer.

Specifically, the generally string-shaped sealant is a sealant having athickness (thickness of the applied sealant or the sealant layer, lengthindicated by Din FIG. 8) satisfying a preferable numerical range and awidth (width of the applied sealant, length indicated by W in FIG. 4 orW₀ in FIG. 6) satisfying a preferable numerical range as describedlater, and more preferably a sealant having a ratio of the thickness tothe width of the sealant [(thickness of sealant)/(width of sealant)]satisfying a preferable numerical range as described later. Thegenerally string-shaped sealant is also a sealant having across-sectional area satisfying a preferable numerical range asdescribed later.

According to the method for producing a self-sealing tire of thisembodiment, the sealant is applied to the inner periphery of the tire bythe following Steps (1) to (3).

<Step (1)>

As shown in FIG. 2, the distance d between the inner periphery 11 of thetire 10 and the tip 31 of the nozzle 30 is measured with the non-contactdisplacement sensor 40 before the application of the sealant 20. Thedistance d is measured for every tire 10 to whose inner periphery 11 isapplied the sealant 20, from the start to the end of application of thesealant 20.

<Step (2)>

The distance d data is transmitted to the controller of the rotary drivedevice. According to the data, the controller controls the amount ofmovement in the radial direction of the tire so that the distancebetween the inner periphery 11 of the tire 10 and the tip 31 of thenozzle 30 is adjusted to a predetermined length.

<Step (3)>

Since the sealant 20 is continuously discharged from the tip 31 of thenozzle 30, it is applied to the inner periphery 11 of the tire 10 afterthe above distance is adjusted. Through the above Steps (1) to (3), thesealant 20 having a uniform thickness can be applied to the innerperiphery 11 of the tire 10.

FIG. 3 is an explanatory view schematically showing the positionalrelationship of the nozzle to the tire.

As shown in FIG. 3, the sealant can be applied while maintaining thedistance between the inner periphery 11 of the tire 10 and the tip 31 ofthe nozzle 30 at a predetermined distance d₀ during the movement of thenozzle 30 to positions (a) to (d) relative to the tire 10.

In order to provide more suitable effects, the controlled distance d₀ ispreferably 0.3 mm or more, more preferably 1.0 mm or more. If thedistance is less than 0.3 mm, the tip of the nozzle is too close to theinner periphery of the tire, which makes it difficult to allow theapplied sealant to have a predetermined thickness. The controlleddistance d₀ is also preferably 3.0 mm or less, more preferably 2.0 mm orless. If the distance is more than 3.0 mm, the sealant may not beattached well to the tire, thereby resulting in reduced productionefficiency.

The controlled distance d₀ refers to the distance in the radialdirection of the tire between the inner periphery of the tire and thetip of the nozzle after the distance is controlled in Step (2).

In order to provide more suitable effects, the controlled distance d₀ ispreferably 30% or less, more preferably 20% or less of the thickness ofthe applied sealant. The controlled distance d₀ is also preferably 5% ormore, more preferably 10% or more of the thickness of the appliedsealant.

The thickness of the sealant (thickness of the applied sealant or thesealant layer, length indicated by D in FIG. 8) is not particularlylimited. In order to provide more suitable effects, the thickness of thesealant is preferably 1.0 mm or more, more preferably 1.5 mm or more,still more preferably 2.0 mm or more, particularly preferably 2.5 mm ormore. Also, the thickness of the sealant is preferably 10 mm or less,more preferably 8.0 mm or less, still more preferably 5.0 mm or less. Ifthe thickness is less than 1.0 mm, a puncture hole formed in the tire isdifficult to reliably seal. Also, a thickness of more than 10 mm is notpreferred because tire weight increases, although with littleimprovement in the effect of sealing puncture holes. The thickness ofthe sealant can be controlled by varying the rotational speed of thetire, the rate of movement in the width direction of the tire, thedistance between the tip of the nozzle and the inner periphery of thetire, or other factors.

The sealant preferably has a substantially constant thickness (thicknessof the applied sealant or the sealant layer). In this case, thedeterioration of tire uniformity can be further prevented and aself-sealing tire having much better weight balance can be produced.

The substantially constant thickness as used herein means that thethickness varies within a range of 90% to 110%, preferably 95% to 105%,more preferably 98% to 102%, still more preferably 99% to 101%.

In order to reduce clogging of the nozzle so that excellent operationalstability can be obtained and to provide more suitable effects, agenerally string-shaped sealant is preferably used and more preferablyspirally attached to the inner periphery of the tire. However, a sealantnot having a generally string shape may also be used and applied byspraying onto the tire inner periphery.

In the case of a generally string-shaped sealant, the width of thesealant (the width of the applied sealant, length indicated by W in FIG.4) is not particularly limited. In order to provide more suitableeffects, the width of the sealant is preferably 0.8 mm or more, morepreferably 1.3 mm or more, still more preferably 1.5 mm or more. If thewidth is less than 0.8 mm, the number of turns of the sealant around thetire inner periphery may increase, reducing production efficiency. Thewidth of the sealant is also preferably 18 mm or less, more preferably13 mm or less, still more preferably 9.0 mm or less, particularlypreferably 7.0 mm or less, most preferably 6.0 mm or less, still mostpreferably 5.0 mm or less. If the width is more than 18 mm, a weightimbalance may be more likely to occur.

The ratio of the thickness of the sealant (thickness of the appliedsealant or the sealant layer, length indicated by D in FIG. 8) to thewidth of the sealant (width of the applied sealant, length indicated byW in FIG. 4) [(thickness of sealant)/(width of sealant)] is preferably0.6 to 1.4, more preferably 0.7 to 1.3, still more preferably 0.8 to1.2, particularly preferably 0.9 to 1.1. A ratio closer to 1.0 resultsin a sealant having an ideal string shape so that a self-sealing tirehaving high sealing performance can be produced with higherproductivity.

In order to provide more suitable effects, the cross-sectional area ofthe sealant (cross-sectional area of the applied sealant, areacalculated by D×W in FIG. 8) is preferably 0.8 mm² or more, morepreferably 1.95 mm² or more, still more preferably 3.0 mm² or more,particularly preferably 3.75 mm² or more, but preferably 180 mm² orless, more preferably 104 mm² or less, still more preferably 45 mm² orless, particularly preferably 35 mm² or less, most preferably 25 mm² orless.

The width of the area where the sealant is attached (hereinafter alsoreferred to as the width of the attached area or the width of thesealant layer, and corresponding to a length equal to 6×W in FIG. 4 or alength equal to W₁+6×W₀ in FIG. 6) is not particularly limited. In orderto provide more suitable effects, the width is preferably 80% or more,more preferably 90% or more, still more preferably 100% or more, butpreferably 120% or less, more preferably 110% or less, of the treadcontact width.

In order to provide more suitable effects, the width of the sealantlayer is preferably 85% to 115%, more preferably 95% to 105% of thewidth of the breaker of the tire (the length of the breaker in the widthdirection of the tire).

Herein, when the tire is provided with a plurality of breakers, thelength of the breaker in the width direction of the tire refers to thelength of the breaker that is the longest in the width direction of thetire, among the plurality of breakers, in the width direction of thetire.

Herein, the tread contact width is determined as follows. First, ano-load and normal condition tire with a normal internal pressuremounted on a normal rim is contacted with a plane at a camber angle of 0degrees while a normal load is applied to the tire, and then the axiallyoutermost contact positions of the tire are each defined as “contactedge Te”. The distance in the tire axis direction between the contactedges Te and Te is defined as a tread contact width TW. The dimensionsand other characteristics of tire components are determined under theabove normal conditions, unless otherwise stated.

The “normal rim” refers to a rim specified for each tire by standards ina standard system including standards according to which tires areprovided, and may be “standard rim” in JATMA, “design rim” in TRA, or“measuring rim” in ETRTO. Moreover, the “normal internal pressure”refers to an air pressure specified for each tire by standards in astandard system including standards according to which tires areprovided, and may be “maximum air pressure” in JATMA, a maximum valueshown in Table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” inTRA, or “inflation pressure” in ETRTO. In the case of tires forpassenger vehicles, the normal internal pressure is 180 kPa.

The “normal load” refers to a load specified for each tire by standardsin a standard system including standards according to which tires areprovided, and may be “maximum load capacity” in JATMA, a maximum valueshown in Table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” inTRA, or “load capacity” in ETRTO. In the case of tires for passengervehicles, the normal load is 88% of the above-specified load.

The rotational speed of the tire during the application of the sealantis not particularly limited. In order to provide more suitable effects,the rotational speed is preferably 5 m/min or higher, more preferably 10m/min or higher, but preferably 40 m/min or lower, more preferably 30m/min or lower, still more preferably 20 m/min or lower. If therotational speed is lower than 5 m/min or higher than 40 m/min, asealant having a uniform thickness cannot be easily applied.

When a non-contact displacement sensor is used, the risk of troublescaused by adhesion of the sealant to the sensor can be reduced. Thenon-contact displacement sensor is not particularly limited as long asthe sensor can measure the distance between the inner periphery of thetire and the tip of the nozzle. Examples include laser sensors,photosensors, and capacitance sensors. These sensors may be used aloneor in combinations of two or more. For measurement of rubber, lasersensors or photosensors are preferred among these, with laser sensorsbeing more preferred. When a laser sensor is used, the distance betweenthe inner periphery of the tire and the tip of the nozzle can bedetermined as follows: the inner periphery of the tire is irradiatedwith a laser; the distance between the inner periphery of the tire andthe tip of the laser sensor is determined based on the reflection of thelaser; and the distance between the tip of the laser sensor and the tipof the nozzle is subtracted from the determined distance.

The location of the non-contact displacement sensor is not particularlylimited as long as the distance between the inner periphery of the tireand the tip of the nozzle before the application of the sealant can bemeasured. The sensor is preferably attached to the nozzle, morepreferably in a location to which the sealant will not adhere.

The number, size, and other conditions of the non-contact displacementsensor are also not particularly limited.

Since the non-contact displacement sensor is vulnerable to heat, thesensor is preferably protected with a heat insulator or the like and/orcooled with air or the like to avoid the influence of heat from the hotsealant discharged from the nozzle. This improves the durability of thesensor.

Although the first embodiment has been described based on an example inwhich the tire, not the nozzle, is moved in the width and radialdirections of the tire, the nozzle, not the tire, may be moved, or boththe tire and the nozzle may be moved.

The rotary drive device preferably includes a means to increase thewidth of a tire at a bead portion. In the application of the sealant toa tire, increasing the width of the tire at a bead portion allows thesealant to be easily applied to the tire. Particularly when the nozzleis introduced near the inner periphery of the tire mounted on the rotarydrive device, the nozzle can be introduced only by parallel movement ofthe nozzle, which facilitates the control and improves productivity.

Any means that can increase the width of a tire at a bead portion can beused as the means to increase the width of a tire at a bead portion.Examples include a mechanism in which two devices each having aplurality of (preferably two) rolls which have a fixed positionalrelationship with each other are used and the devices move in the widthdirection of the tire. The devices may be inserted from both sidesthrough the opening of the tire into the inside and allowed to increasethe width of the tire at a bead portion.

In the production method, since the sealant which has been mixed in, forexample, a twin screw kneading extruder and in which the crosslinkingreaction in the extruder is suppressed is directly applied to the tireinner periphery, the crosslinking reaction begins upon the applicationand the sealant adheres well to the tire inner periphery and, at thesame time, the crosslinking reaction more suitably proceeds, whereby aself-sealing tire having high sealing performance can be produced. Thus,the self-sealing tire with the sealant applied thereto does not needfurther crosslinking, thereby offering good productivity.

The self-sealing tire with the sealant applied thereto may be furthersubjected to a crosslinking step, if necessary.

The self-sealing tire is preferably heated in the crosslinking step.This improves the rate of crosslinking of the sealant and allows thecrosslinking reaction to more suitably proceed so that the self-sealingtire can be produced with higher productivity. The tire may be heated byany method, including known methods, but it may suitably be heated in anoven. The crosslinking step may be carried out, for example, by placingthe self-sealing tire in an oven at 70° C. to 190° C., preferably 150°C. to 190° C., for 2 to 15 minutes.

The tire is preferably rotated in the circumferential direction of thetire during the crosslinking because then flowing of even thejust-applied, easily flowing sealant can be prevented and thecrosslinking reaction can be accomplished without deterioration ofuniformity. The rotational speed is preferably 12 to 1,000 rpm, morepreferably 12 to 200 rpm. Specifically, for example, an oven equippedwith a rotational mechanism may be used.

Even when the crosslinking step is not additionally performed, the tireis preferably rotated in the circumferential direction of the tire untilthe crosslinking reaction of the sealant is completed. In this case,flowing of even the just-applied, easily flowing sealant can beprevented and the crosslinking reaction can be accomplished withoutdeterioration of uniformity. The rotational speed is the same asdescribed for the crosslinking step.

In order to improve the rate of crosslinking of the sealant, the tire ispreferably preliminarily warmed before the application of the sealant.In this case, a self-sealing tire can be produced with higherproductivity. The temperature for pre-heating the tire is preferably 40°C. to 100° C., more preferably 50° C. to 70° C. When the tire ispre-heated within the temperature range indicated above, thecrosslinking reaction suitably begins upon the application and moresuitably proceeds so that a self-sealing tire having high sealingperformance can be produced. Moreover, when the tire is pre-heatedwithin the temperature range indicated above, the crosslinking step isnot necessary and thus a self-sealing tire can be produced with highproductivity.

In general, continuous kneaders (especially twin screw kneadingextruders) are continuously operated. In the production of self-sealingtires, however, tires need to be replaced one after another uponcompletion of the application of the sealant to one tire. Here, in orderto produce a higher quality self-sealing tire while reducing thedeterioration of productivity, the following method (1) or (2) may beused. The method (1) or (2) may be appropriately selected depending onthe situation, in view of the following disadvantages: a deteriorationin quality in the method (1) and an increase in cost in the method (2).

(1) The feed of the sealant to the inner periphery of the tire iscontrolled by running or stopping the continuous kneader and all thefeeders simultaneously.

Specifically, upon completion of the application to one tire, thecontinuous kneader and all the feeders may be simultaneously stopped,the tire may be replaced with another tire, preferably within oneminute, and the continuous kneader and all the feeders may besimultaneously allowed to run to restart the application to the tire. Byreplacing tires quickly, preferably within one minute, the deteriorationin quality can be reduced.

(2) The feed of the sealant to the inner periphery of the tire iscontrolled by switching flow channels while allowing the continuouskneader and all the feeders to keep running.

Specifically, the continuous kneader may be provided with another flowchannel in addition to the nozzle for direct feeding to the tire innerperiphery, and the prepared sealant may be discharged from the anotherflow channel after completion of the application to one tire untilcompletion of the replacement of tires. According to this method, sincea self-sealing tire can be produced while the continuous kneader and allthe feeders are kept running, the produced self-sealing tire can havehigher quality.

Non-limiting examples of carcass cords that can be used in the carcassof the self-sealing tire include fiber cords and steel cords. Steelcords are preferred among these. In particular, steel cords formed ofhard steel wire materials specified in JIS G 3506 are desirable. The useof strong steel cords, instead of commonly used fiber cords, as carcasscords in the self-sealing tire can greatly improve side cut resistance(resistance to cuts formed in the tire side portions due to driving overcurbs or other reasons) and thereby further improve the punctureresistance of the entire tire including the side portions.

The steel cord may have any structure. Examples include steel cordshaving a 1×n single strand structure, steel cords having a k+m layerstrand structure, steel cords having a 1×n bundle structure, and steelcords having an m×n multi-strand structure. The term “steel cord havinga 1×n single strand structure” refers to a single-layered twisted steelcord prepared by intertwining n filaments. The term “steel cord having ak+m layer strand structure” refers to a steel cord having a two-layeredstructure in which the two layers are different from each other in twistdirection and twist pitch, and the inner layer includes k filamentswhile the outer layer includes m filaments. The term “steel cord havinga 1×n bundle structure” refers to a bundle steel cord prepared byintertwining bundles of n filaments. The term “steel cord having an m×nmulti-strand structure” refers to a multi-strand steel cord prepared byintertwining m strands prepared by first twisting n filaments together.Here, n represents an integer of 1 to 27; k represents an integer of 1to 10; and m represents an integer of 1 to 3.

The twist pitch of the steel cord is preferably 13 mm or less, morepreferably 11 mm or less, but preferably 5 mm or more, more preferably 7mm or more.

The steel cord preferably contains at least one piece of preformedfilament formed in the shape of a spiral. Such a preformed filamentprovides a relatively large gap within the steel cord to improve rubberpermeability and also maintain the elongation under low load, so that amolding failure during vulcanization can be prevented.

The surface of the steel cord is preferably plated with brass, Zn, orother materials to improve initial adhesion to the rubber composition.

The steel cord preferably has an elongation of 0.5% to 1.5% under a loadof 50 N. If the elongation under a load of 50 N is more than 1.5%, thereinforcing cords may exhibit reduced elongation under high load andthus disturbance absorption may not be maintained. Conversely, if theelongation under a load of 50 N is less than 0.5%, the cords may notexhibit sufficient elongation during vulcanization and thus a moldingfailure may occur. In view of the above, the elongation under a load of50 N is more preferably 0.7% or more, but more preferably 1.3% or less.

The endcount of the steel cords is preferably 20 to 50 (ends/5 cm).

Second Embodiment

The studies of the present inventors have further revealed that the useof the method according to the first embodiment alone has the followingdisadvantage: a sealant having a generally string shape is occasionallydifficult to attach to the inner periphery of a tire and can easily peeloff especially at the attachment start portion. A second embodiment ischaracterized in that in the method for producing a self-sealing tire,the sealant is first attached under conditions where the distancebetween the inner periphery of the tire and the tip of the nozzle isadjusted to a distance d₁ and then to a distance d₂ larger than thedistance d₁. In this case, the distance between the inner periphery ofthe tire and the tip of the nozzle is shortened at the beginning of theattachment, so that the width of the sealant corresponding to theattachment start portion can be increased. As a result, a self-sealingtire can be easily produced in which a generally string-shaped adhesivesealant is continuously and spirally attached at least to the innerperiphery of the tire that corresponds to a tread portion, and at leastone of the longitudinal ends of the sealant forms a wider portion havinga width larger than that of the longitudinally adjoining portion. Inthis self-sealing tire, a portion of the sealant that corresponds tostarting of attachment has a larger width to improve adhesion of thisportion so that peeling of this portion of the sealant can be prevented.

The description of the second embodiment basically includes onlyfeatures different from the first embodiment, and the contentsoverlapping the description of the first embodiment are omitted.

FIG. 5 are enlarged views showing the vicinity of the tip of the nozzleincluded in the applicator shown in FIG. 1. FIG. 5(a) illustrates astatus immediately after attachment of the sealant is started and FIG.5(b) illustrates a status after a lapse of a predetermined time.

FIG. 5 each show a cross section of a part of a tire 10 taken along aplane including the circumferential and radial directions of the tire.In FIG. 5, the width direction (axis direction) of the tire is indicatedby an arrow X, the circumferential direction of the tire is indicated byan arrow Y, and the radial direction of the tire is indicated by anarrow Z.

According to the second embodiment, the tire 10 formed through avulcanization step is first mounted on a rotary drive device, and anozzle 30 is inserted into the inside of the tire 10. Then, as shown inFIG. 1 and FIG. 5, the tire 10 is rotated and simultaneously moved inthe width direction while a sealant 20 is discharged from the nozzle 30,whereby the sealant is continuously applied to the inner periphery 11 ofthe tire 10. The tire 10 is moved in the width direction according to,for example, the pre-entered profile of the inner periphery 11 of thetire 10.

Since the sealant 20 is adhesive and has a generally string shape, thesealant 20 is continuously and spirally attached to the inner periphery11 of the tire 10 that corresponds to a tread portion.

In this process, as shown in FIG. 5(a), the sealant 20 is attached underconditions where the distance between the inner periphery 11 of the tire10 and the tip 31 of the nozzle 30 is adjusted to a distance d₁ for apredetermined time from the start of the attachment. Then, after a lapseof the predetermined time, as shown in FIG. 5(b), the tire 10 is movedin the radial direction to change the distance to a distance d₂ largerthan the distance d₁ and the sealant 20 is attached.

The distance may be changed from the distance d₂ back to the distance d₁before completion of the attachment of the sealant. In view ofproduction efficiency and tire weight balance, the distance d₂ ispreferably maintained until the sealant attachment is completed.

Preferably, the distance d₁ is kept constant for a predetermined timefrom the start of the attachment, and after a lapse of the predeterminedtime the distance d₂ is kept constant, although the distances d₁ and d₂are not necessarily constant as long as they satisfy the relation ofd₁<d₂.

The distance d₁ is not particularly limited. In order to provide moresuitable effects, the distance d₁ is preferably 0.2 mm or more, morepreferably 0.3 mm or more, still more preferably 0.5 mm or more. If thedistance d₁ is less than 0.2 mm, the tip of the nozzle is too close tothe inner periphery of the tire, so that the sealant can easily adhereto the nozzle and the nozzle may need to be cleaned more frequently. Thedistance d₁ is also preferably 2 mm or less, more preferably 1 mm orless. If the distance d₁ is more than 2 mm, the effect produced by theformation of a wider portion may not be sufficient.

The distance d₂ is also not particularly limited. In order to providemore suitable effects, the distance d₂ is preferably 0.3 mm or more,more preferably 1 mm or more, but preferably 3 mm or less, morepreferably 2 mm or less. The distance d₂ is preferably the same as thecontrolled distance d₀ described above.

Herein, the distances d₁ and d₂ between the inner periphery of the tireand the tip of the nozzle each refer to the distance in the radialdirection of the tire between the inner periphery of the tire and thetip of the nozzle.

The rotational speed of the tire during the attachment of the sealant isnot particularly limited. In order to provide more suitable effects, therotational speed is preferably 5 m/min or higher, more preferably 10m/min or higher, but preferably 40 m/min or lower, more preferably 30m/min or lower, still more preferably 20 m/min or lower. If therotational speed is lower than 5 m/min or higher than 40 m/min, asealant having a uniform thickness cannot be easily attached.

The self-sealing tire according to the second embodiment can be producedthrough the steps described above.

FIG. 6 is an explanatory view schematically showing an example of asealant attached to a self-sealing tire according to the secondembodiment.

The generally string-shaped sealant 20 is wound in the circumferentialdirection of the tire and continuously and spirally attached. Here, oneof the longitudinal ends of the sealant 20 forms a wider portion 21having a width larger than that of the longitudinally adjoining portion.The wider portion 21 corresponds to the attachment start portion of thesealant.

The width of the wider portion of the sealant (width of the widerportion of the applied sealant, length indicated by W₁ in FIG. 6) is notparticularly limited. In order to provide more suitable effects, thewidth of the wider portion is preferably 103% or more, more preferably110% or more, still more preferably 120% or more of the width of thesealant other than the wider portion (length indicated by W₀ in FIG. 6).If it is less than 103%, the effect produced by the formation of a widerportion may not be sufficient. The width of the wider portion of thesealant is also preferably 210% or less, more preferably 180% or less,still more preferably 160% or less of the width of the sealant otherthan the wider portion. If it is more than 210%, the tip of the nozzleneeds to be placed excessively close to the inner periphery of the tireto form a wider portion, with the result that the sealant can easilyadhere to the nozzle and the nozzle may need to be cleaned morefrequently. In addition, tire weight balance may be impaired.

The width of the wider portion of the sealant is preferablysubstantially constant in the longitudinal direction but may partiallybe substantially not constant. For example, the wider portion may have ashape in which the width is the largest at the attachment start portionand gradually decreases in the longitudinal direction. The substantiallyconstant width as used herein means that the width varies within a rangeof 90% to 110%, preferably 97% to 103%, more preferably 98% to 102%,still more preferably 99% to 101%.

The length of the wider portion of the sealant (length of the widerportion of the applied sealant, length indicated by L₁ in FIG. 6) is notparticularly limited. In order to provide more suitable effects, thelength is preferably less than 650 mm, more preferably less than 500 mm,still more preferably less than 350 mm, particularly preferably lessthan 200 mm. If the length is 650 mm or more, the tip of the nozzle isplaced close to the inner periphery of the tire for a longer period oftime, so that the sealant can easily adhere to the nozzle and the nozzlemay need to be cleaned more frequently. In addition, tire weight balancemay be impaired. The sealant preferably has a shorter wider portion.However, for control of the distance between the inner periphery of thetire and the tip of the nozzle, the limit of the length of the widerportion is about 10 mm.

The width of the sealant other than the wider portion (width of theapplied sealant other than the wider portion, length indicated by W₀ inFIG. 6) is not particularly limited. In order to provide more suitableeffects, the width is preferably 0.8 mm or more, more preferably 1.3 mmor more, still more preferably 1.5 mm or more. If the width is less than0.8 mm, the number of turns of the sealant around the inner periphery ofthe tire may increase, reducing production efficiency. The width of thesealant other than the wider portion is also preferably 18 mm or less,more preferably 13 mm or less, still more preferably 9.0 mm or less,particularly preferably 7.0 mm or less, most preferably 6.0 mm or less,still most preferably 5.0 mm or less. If the width is more than 18 mm, aweight imbalance may be more likely to occur. W₀ is preferably the sameas the above-described W.

The width of the sealant other than the wider portion is preferablysubstantially constant in the longitudinal direction but may partiallybe substantially not constant.

The width of the area where the sealant is attached (hereinafter alsoreferred to as the width of the attached area or the width of thesealant layer, and corresponding to a length equal to W₁+6×W₀ in FIG. 6)is not particularly limited. In order to provide more suitable effects,the width is preferably 80% or more, more preferably 90% or more, stillmore preferably 100% or more, but preferably 120% or less, morepreferably 110% or less, of the tread contact width.

In order to provide more suitable effects, the width of the sealantlayer is preferably 85% to 115%, more preferably 95% to 105% of thewidth of the breaker of the tire (length of the breaker in the widthdirection of the tire).

In the self-sealing tire according to the second embodiment, the sealantis preferably attached without overlapping in the width direction, morepreferably without gaps.

In the self-sealing tire according to the second embodiment, the otherlongitudinal end (the end corresponding to the attachment endingportion) of the sealant may also form a wider portion having a widthlarger than that of the longitudinally adjoining portion.

The thickness of the sealant (thickness of the applied sealant or thesealant layer, length indicated by D in FIG. 8) is not particularlylimited. In order to provide more suitable effects, the thickness of thesealant is preferably 1.0 mm or more, more preferably 1.5 mm or more,still more preferably 2.0 mm or more, particularly preferably 2.5 mm ormore, but preferably 10 mm or less, more preferably 8.0 mm or less,still more preferably 5.0 mm or less. If the thickness is less than 1.0mm, a puncture hole formed in the tire is difficult to reliably seal.Also, a thickness of more than 10 mm is not preferred because tireweight increases, although with little improvement in the effect ofsealing puncture holes.

The sealant preferably has a substantially constant thickness (thicknessof the applied sealant or the sealant layer). In this case, thedeterioration of tire uniformity can be further prevented and aself-sealing tire having much better weight balance can be produced.

The ratio of the thickness of the sealant (thickness of the appliedsealant or the sealant layer, length indicated by D in FIG. 8) to thewidth of the sealant other than the wider portion (width of the appliedsealant other than the wider portion, length indicated by W₀ in FIG. 6)[(thickness of sealant)/(width of sealant other than wider portion)] ispreferably 0.6 to 1.4, more preferably 0.7 to 1.3, still more preferably0.8 to 1.2, particularly preferably 0.9 to 1.1. A ratio closer to 1.0results in a sealant having an ideal string shape so that a self-sealingtire having high sealing performance can be produced with higherproductivity.

In order to provide more suitable effects, the cross-sectional area ofthe sealant (cross-sectional area of the applied sealant, areacalculated by D×W in FIG. 8) is preferably 0.8 mm² or more, morepreferably 1.95 mm² or more, still more preferably 3.0 mm² or more,particularly preferably 3.75 mm² or more, but preferably 180 mm² orless, more preferably 104 mm² or less, still more preferably 45 mm² orless, particularly preferably 35 mm² or less, most preferably 25 mm² orless.

According to the second embodiment, even when the sealant has aviscosity within the range indicated earlier, and particularly arelatively high viscosity, widening a portion of the sealant thatcorresponds to starting of attachment can improve adhesion of thisportion so that peeling of this portion of the sealant can be prevented.

The self-sealing tire according to the second embodiment is preferablyproduced as described above. However, the self-sealing tire may beproduced by any other appropriate method as long as at least one of theends of the sealant is allowed to form a wider portion.

Although the above descriptions, and particularly the description of thefirst embodiment, explain the case where a non-contact displacementsensor is used in applying the sealant to the inner periphery of thetire, the sealant may be applied to the inner periphery of the tirewhile controlling the movement of the nozzle and/or the tire accordingto the pre-entered coordinate data without measurement using anon-contact displacement sensor.

EXAMPLES

The present invention is specifically described with reference to, butnot limited to, examples below.

The chemicals used in the examples are listed below.

Butyl rubber: IIR065 available from JSR Corporation

Polybutene: HV-1900 available from JX Nippon Oil & Energy Corporation,number average molecular weight: 2,900

Carbon black: N330 available from Cabot Japan K.K.

Oil: DOS (dioctyl sebacate) available from Taoka Chemical Co., Ltd.

Crosslinking agent: NYPER NS (BPO: 40%, DBP: 48%) available from NOFCorporation

Crosslinking activator: Q0 (quinone dioxime) available from Ouchi ShinkoChemical Industrial Co., Ltd.

<Preparation of Sealants>

A sealant was prepared by kneading the raw materials according to theformulation shown in Table 1 at 120° C. using a twin screw kneadingextruder.

TABLE 1 Formulation Raw material (parts by mass) Butyl rubber 100Polybutene 200 Carbon black 15 Oil 15 Crosslinking agent 7 Crosslinkingactivator 7

EXAMPLES AND COMPARATIVE EXAMPLE

The sealant (viscosity at 40° C.: 20,000 Pa·s) was extruded from a twinscrew kneading extruder and attached through a nozzle to the innerperiphery of a tire (235/45R17, 94W, outer diameter: 643 mm, treadcontact width: 200 mm, vulcanized, tire rotational speed: 12 m/min,pre-heating temperature: 40° C.) mounted on a rotary drive device, sothat the attached sealant had a thickness of 3 mm and the width of theattached area was 210 mm (105% of the tread contact width) to prepare aself-sealing tire. In this process, the approach distance between thetip of the nozzle and the inner periphery of the tire and its durationwere controlled at the beginning of the attachment so that the width andlength of the wider portion of the attached sealant and the width of thesealant other than the wider portion were adjusted as shown in Table 2.The width of the wider portion and the width of the sealant other thanthe wider portion were adjusted so as to be substantially constant inthe longitudinal direction. The viscosity of the sealant was measured at40° C. in conformity with JIS K 6833 using a rotational viscometer. Thediameter of the discharge port of the nozzle (nozzle diameter) was setas follows: Example 6: 0.8 mm; Example 7: 1.2 mm; Example 8: 5.0 mm;Example 9: 7.0 mm; and other examples: 3.0 mm.

<Evaluation Items and Test Methods>

The prepared self-sealing tires were evaluated for the items below.Table 2 shows the results.

(Attachment Success Rate)

Ten self-sealing tires (n=10) were prepared in each example orcomparative example and visually observed to determine whether theattachment start portion of the sealant was peeled. Tires without andwith sealant peeling were rated as “success” and “failure”,respectively, based on which the success rate (%) of the attachment ofthe sealant was determined. A higher rate indicates better adhesion ofthe sealant. A rate of 80% or higher was considered to be good.

(Amount of Imbalance)

The weight balance of each tire before the attachment of the sealant wasmeasured with a common balancer and then controlled based on themeasurement. After the sealant was attached, the weight balance of thetire was again measured to determine the amount of additional weight.The average of the amounts of additional weight (n=10) was taken as theamount (g) of imbalance in each example or comparative example. Asmaller value indicates better weight balance. An amount of 5 g orsmaller was considered to be good.

(Cleaning Frequency)

Self-sealing tires were produced under the same conditions in eachexample or comparative example to determine the number of tires producedbefore the nozzle needed to be cleaned, which was taken as the nozzlecleaning frequency (expressed in the number of tires). A larger valueindicates lower frequency of cleaning. Frequencies of at least 3 tiresand of at least 8 tires were considered to be good and especially good,respectively. When the nozzle did not need cleaning in the production offifty self-sealing tires under the same conditions, the nozzle cleaningfrequency was displayed as “unnecessary”.

TABLE 2 Com. Unit Ex. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Length of m 101 101 101 101 101101 404 269 51 40 101 101 101 101 101 attachment to tire Width of mm 4 67 8 5 4.2 1.5 2.25 12.75 15 6 6 6 6 6 wider portion (a) Width of mm 4 44 4 4 4 1 1.5 8.5 10 4 4 4 4 4 portion other than wider portion (b)(a)/(b) % 100 150 175 200 125 105 150 150 150 150 150 150 150 150 150Length of mm — 150 150 150 150 150 150 150 150 150 10 100 300 400 600wider portion d1 mm 2.0 1.0 0.5 0.2 1.3 1.9 1.0 1.0 1.0 1.0 1.0 1.0 1.01.0 1.0 d2 mm 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.02.0 Attachment % 10 100 100 100 100 90 100 100 100 100 100 100 100 100100 success rate Amount of g 0 0 0 0 0 0 0 0 1 3 0 0 0 0 0 imbalanceNozzle tires Unnec- 10 9 3 12 16 10 10 10 10 20 16 9 8 3 cleaning essaryfrequency

The results in Table 2 demonstrate that, in the case of the self-sealingtires of the examples in which at least one of the longitudinal ends ofthe sealant formed a wider portion having a width larger than that ofthe longitudinally adjoining portion, the attachment success rate washigh and peeling of this portion of the sealant was prevented.

The results further demonstrate that when the width and length of thewider portion of the attached sealant and the width of the sealant otherthan the wider portion were adjusted within specific ranges,self-sealing tires having good weight valance were obtained and thenozzle cleaning frequency in the production of the self-sealing tireswas also reduced.

REFERENCE SIGNS LIST

-   10 Tire-   11 Inner periphery of tire-   14 Tread portion-   15 Carcass-   16 Breaker-   17 Band-   20 Sealant-   21 Wider portion-   30 Nozzle-   31 Tip of nozzle-   40 Non-contact displacement sensor-   50 Rotary drive device-   60 Twin screw kneading extruder-   61 (61 a, 61 b, 61 c) Supply port-   62 Material feeder-   d, d₀, d₁, d₂ Distance between inner periphery of tire and tip of    nozzle

The invention claimed is:
 1. A pneumatic tire, comprising a generallystring-shaped adhesive sealant, wherein the sealant is continuously andspirally attached at least to an inner periphery of the tire thatcorresponds to a tread portion to form a sealant layer, the sealant hasa wider portion on at least one of longitudinal ends thereof, each widerportion having a width larger than that of the remaining portion, thesealant layer is formed of the generally string-shaped sealant providedcontinuously and spirally along the inner periphery of the tire, and theremaining portion has a constant width and the width of each widerportion is 103% to 180% of the width of the remaining portion.
 2. Thepneumatic tire according to claim 1, wherein the remaining portion has awidth of 1.3 to 13 mm.
 3. The pneumatic tire according to claim 1,wherein each wider portion of the sealant has a length shorter than 500mm.
 4. The pneumatic tire according to claim 1, wherein the area wherethe sealant is attached has a width that is 80% to 120% of the treadcontact width.
 5. The pneumatic tire according to claim 1, wherein thesealant has a thickness of 1 to 10 mm.
 6. A method for producing apneumatic tire according to claim 1, the method comprising dischargingthe generally string-shaped adhesive sealant from a nozzle tocontinuously and spirally attach the sealant at least to the innerperiphery of the tire that corresponds to the tread portion to form thesealant layer, the sealant being attached under conditions where adistance between the inner periphery of the tire and a tip of the nozzleis adjusted to a distance di and then to a distance d2 larger than thedistance di so that the at least one of longitudinal ends of the sealantforms each wider portion having a width larger than that of theremaining portion.
 7. The method for producing a pneumatic tireaccording to claim 6, wherein the sealant is extruded from a twin screwkneading extruder and fed to the nozzle.